Compound pump

ABSTRACT

The invention relates to a friction vacuum pump ( 1 ) containing at least one turbomolecular pump stage ( 6, 7 ), a screw pump stage ( 11, 12 ) connected to the delivery side of the pump, and a filling stage ( 24 ) arranged between the turbomolecular pump stage ( 6, 7 ) and the screw pump stage ( 11, 12 ). According to the invention it is proposed that said filling stage ( 24 ) be configured as a centrifugal stage in order to simplify the construction thereof.

BACKGROUND OF THE INVENTION

The present invention relates to a friction vacuum pump containing atleast one turbomolecular pump stage, a screw pump stage connected on thedelivery side of the pump, and a filling stage arranged between theturbomolecular pump stage and the screw pump stage.

In turbomolecular pumps with downstream screw pump stages, which arealso called compound pumps, the pumped gas needs to be transferred froma pump chamber having a relatively large volume in which the axialcompressor stages are located, into a pump chamber (pumping slot) havinga relatively small volume in which the screw is located. Known designsfor this transitional area have the disadvantage that the flow willbreakdown. This will significantly impair the pumping capacity of thepump.

From DE-A-196 32 874 it is known to provide between the turbomolecularpump stage and the downstream screw pump stage, a filling stage which isequipped with blades. The production of such an intermediate stage isinvolved. Moreover, the presence of the blades will hamper assembly.

SUMMARY OF THE INVENTION

It is the task of the present invention to considerably simplify thedesign of the filling stage without impairing the effective supply ofgas into the screw pump stage.

This task is solved through the present invention by designing thefilling stage as a centrifugal stage. Components of the centrifugalstage are rotating ridges which are located at the level of the intakearea of the screw pump stage. The centrifugal pump has the effect ofdeflecting and compressing the gas ejected by the turbomolecular pumpstage and supplying the gas into the pump chamber of the screw pump. Thegas flow is substantially continuous so that the flow will no longerbreakdown thereby impairing operation.

Owing to the fact that the centrifugal stage deflects the gas flowoutwards, there exists the possibility of selecting a relatively largediameter for the pumping slot of the screw pump stage, so that therotating pumping surface of the screw pump stage has a highcircumferential speed.

If the inside diameter of the stator at the outside of the screw pumpstage is greater than the outside diameter of the rotor of theturbomolecular pump stage, then there exists, provided that the statorof the turbomolecular pump consists of spacing rings and bladehalf-rings in a basically known manner, the possibility of being able toassemble or disassemble the stator of both pump stages without the needto assemble resp. disassemble the rotor of the turbomolecular pumpstage. These dimensions will allow the rotary system of the compoundpump to be balanced first, followed by subsequent assembly of the statorcomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and details of the present invention shall beexplained with reference to the design examples depicted in drawingFIGS. 1 to 5. Depicted in drawing

FIG. 1 is a partial longitudinal sectional view through a design examplefor a friction vacuum pump according to the present invention and

FIGS. 2, 3, 4 and 5 top views on different variants for the centrifugalstage.

In the design example according to drawing FIG. 1, the pump itself isdesignated as 1, its inlet with 2 and its discharge with 3. The housingof the pump comprises the two sections 4 and 5.

DESCRIPTION OF THE INVENTION

Housing section 4 embraces the stator 6 and the rotor 7 of theturbomolecular pump stage. The stator 6 comprises the only schematicallyindicated blade half-rings 8 as well as spacing rings 9, which togetherform a self-centering stator pack. The rotor 7 is equipped with rotorblades 10.

Housing section 4 also embraces the stator 11 and the rotor 12 of thescrew pump stage, the pumping chamber or slot of which is designated as13. The thread 14 of this stage may be arranged on the side of thestator or the rotor. In the case of the depicted design example it isarranged on the side of the stator and is part of a stator sleeve 15which may be fitted independently of the housing section. The rotor 7 ofthe turbomolecular pump stage 7, 8 and the rotor 12 of the screw pumpstage 11, 12 are components of a jointly rotating system 7, 12. Therotor 12 and the screw pump stage 11, 12 form the end of this system onthe delivery side and may be designed as a disk or bell-shaped (asdepicted in drawing FIG. 1).

Housing section 5 embraces the drive motor 16, the stator of which isdesignated as 17 and its rotor as 18. Housing section 5 is part of achassis 19 with an internal chamber, in which the drive motor 16 andfurther components are located. Also located in chassis 19 are thebearings for the shaft 21 carrying the rotors 7 and 12 of the compoundpump. Only the upper bearing 22 is depicted. Moreover, the chassis 19 isthe carrier for all further components of pump 1.

In the assembled state of pump 1 the housing sections are linked to eachother. The stator sleeve 15 is supported by chassis 19. The insidediameter is slightly greater than the outside diameter of rotor 7 of theturbomolecular pump stage so that the stator sleeve 15 may bedisassembled after having removed housing section 4 and withdisassembled stator 6 of the turbomolecular pump stage 6, 7. Thus thereexists the possibility of being able to assemble all stator components8, 9, 15 after assembly of the rotating system 7, 12 and also afterbalancing it.

Placed on the face side of stator sleeve 15 at the intake side is animpeller 23, the inside rim of which corresponds to the inside diameterof the spacing rings 9. In the assembled state of the pump, the statorpack 6 is supported by the impeller 23.

Located between the turbomolecular pump stage 6, 7 and the screw pumpstage 11, 12 is a filling stage which is designed as a centrifugal stage24. It comprises ridges 25 which extend basically radially towards theoutside, these ridges forming pockets 26 facing the last row of rotorblades. Various design implementations of the centrifugal stage 24 aredepicted in drawing FIGS. 2 to 5. Located between the ridges 25 are thepockets 26, said pockets being open towards the top and the outside. Thearrow 27 indicates in each case the direction of rotation.

In the design example presented, the centrifugal stage 24 is part of therotor 12 of the screw pump stage. Said centrifugal stage is arranged onthe side facing the blades 10 of the turbomolecular pump stage 7, 10 ofthe disk or bell-shaped rotor 12.

The depth of the pockets 26 may increase radially towards the outside(drawing FIG. 1). Their location is so selected that the peripheralopenings of the pockets 26 are arranged at the level of the inlet of thescrew pump stage 11, 12. In the design implementation according todrawing FIG. 2, the ridges extend radially. In the designimplementations according to drawing FIGS. 3 and 4, the ridges 25 areinclined backwards with respect to the direction of rotation 27, and inthe design implementation according to drawing FIG. 5 they are inclinedto the front. The discharge angle of the ridges (blade of thecentrifugal stage) defines the static and dynamic share in the pressurelevel. If the ridge bends backwards, a high static share will result.Moreover, the degree of deflection in the circumferential direction isincreased by a backwards bend. If the ridge bends forwards, a highdynamic share will result.

From drawing FIG. 1 it is also apparent that the radial dimensions ofthe pockets 26 substantially correspond to the active pumping lengths ofthe blades 10 of the last row of rotor blades located on the deliveryside. In the centrifugal stage 24, the gases leaving the turbomolecularpump stage are deflected, owing to the effect of the ridges 26 andpockets 27, specifically in the direction of the pumping slot 13 of thescrew pump stage 11, 12. At the same time a compression is effected sothat flow breakdowns are largely avoided.

What is claimed is:
 1. A compound vacuum pump assembly that includes: a turbomolecular pump stage having an inlet for delivering a fluid into the pump assembly and an outlet section, a centrifugal pump stage; and a screw pump stage having an inlet and an outlet for discharging fluid from the assembly; said stages being aligned in a series along a common axis and sharing a common rotor; said screw pump stage containing a stator and said inlet of said screw pump stage being located adjacent to said outlet of said turbomolecular pump stage and; said centrifugal pump stage having an impeller mounted upon said rotor that is positioned inside the stator of said screw pump stage at the inlet to said screw pump stage, said impeller having radially extended blades that form radially extended pockets facing the outlet of said turbomolecular pump stage and being arranged to turn the fluid leaving the turbomolecular pump radially into the inlet of the screw pump stage.
 2. The pump assembly of claim 1 wherein the turbomolecular pump stage contains a stator having a diameter that is smaller than the diameter of the screw pump stage stator.
 3. The pump assembly of claim 1 wherein the rotor sections of each pump stage are integrally joined.
 4. The pump assembly of claim 1 wherein said pockets expand radially toward the outer periphery of the impeller.
 5. The pump assembly of claim 1 wherein said blades curve forwardly with respect to the direction of rotation of said impeller.
 6. The pump assembly of claim 1 wherein said blades curve rearward with respect to the direction of rotation of said impeller.
 7. The pump assembly of claim 1 wherein said impeller is integral with said rotor. 